The invention relates to improvements in methods and apparatus for ascertaining the diameters of rod-shaped articles, particularly rod-shaped articles of the tobacco processing industry. Such articles include tobacco-containing rods, rods of filter material for tobacco smoke, sections of filter rods, sections of tobacco-containing rods as well as filter cigarettes, cigarillos, cigars and cheroots.
It is already known to ascertain the diameters of rod-shaped articles by placing the articles onto a support which transports the articles through a measuring station wherein the diameter of each article is ascertained by resorting to a beam of light or other suitable radiation.
The diameter constitutes an important parameter of each rod-shaped article of the tobacco processing industry. The same holds true for the shape of each rod-shaped article, i.e., it is important that the diameter match or closely approach a selected optimum diameter and that the shape of each article at least approximate a desired shape. For example, many plain or filter cigarettes are or should be round. On the other hand, certain manufacturers prefer to turn out rod-shaped articles of the tobacco processing industry which have a slightly oval shape. In either event, it is desirable and advantageous to monitor the rod-shaped articles in order to rapidly detect deviations from the desired or optimal diameter and/or from the desired or optimal cross-sectional outline.
In accordance with a presently preferred procedure, the diameters of successive rod-shaped articles of the tobacco processing industry (hereinafter generically referred to as cigarettes or filter cigarettes but intended to embrace also filter rod sections, cigars and others) are ascertained by transporting successive cigarettes past a photoelectronic detector wherein a beam of radiation issuing from a suitable source and directed upon an optoelectronic signal generating transducer crosses the path of successive cigarettes. The diameters of successive cigarettes are ascertained by determining the duration of transport of a cigarette across the beam of radiation and by taking into consideration the speed of transport of the cigarettes through the monitoring station. Thus, if the speed of advancement of cigarettes across the beam is fixed or constant, the duration of interval of interruption or interception of the beam by a cigarette is directly related to the diameter of such cigarette.
A drawback of the just outlined procedure is that the results of measurement are misleading if the cigarette which intercepts the beam for a certain interval of time is out of round or is otherwise deformed. Attempts to overcome such problem include the utilization of two photoelectronic detectors with crossing beams of optical radiation. Thus, each detector ascertains a different diameter of each article and the difference (if any) between the thus determined different diameters of an article is then indicative of the degree and/or nature of deformation of the respective article. Reference may be had, for example, to U.S. Pat. No. 4,011,950 granted Mar. 15, 1977 to McLoughlin et al. for "Cigarette Monitoring Apparatus".
The proposal of McLoughlin et al. also exhibits certain drawbacks, perhaps primarily because the apparatus which is disclosed in this patent does not permit the determination of two diameters which extend at right angles to each other. As a rule, diameter measurements with two photoelectronic detectors are carried out in such a way that the two ascertained diameters make an angle of less than 90.degree.. This renders it necessary to employ rather complex signal evaluating systems or to disregard certain errors which develop as a result of the failure to determine two diameters which are exactly normal to each other. On the other hand, it is highly desirable and advantageous to ascertain the diameters of cigarettes with a very high degree of accuracy, for example, when the cigarettes and filter rod sections are fed into a tipping machine wherein each filter rod section is united with one or more plain cigarettes to form therewith a filter cigarette of unit length or multiple unit length.